JP3522560B2 - Method of manufacturing protective tube for measuring instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a protective tube for a measuring instrument, and more particularly to a method for pyrolyzing a petroleum hydrocarbon in a cracking furnace, separating and purifying it, and rectifying it to obtain ethylene or propylene (hereinafter referred to as "olefin"). This is a new proposal for a method for surface treatment of thermometer protection tubes installed in a plant that manufactures a thermometer. In the present invention, the surface treatment technology employed is a surface treatment technology for a site where erosion damage occurs due to fly ash generated in coal gasification, liquefaction plant, coal combustion boiler plant or the like, or an erosion damage site generated by water slurry. Also available as

[0002]

2. Description of the Related Art Generally, a cracking furnace for thermally cracking petroleum hydrocarbons is used in a process for producing olefins or the like. This decomposition furnace is provided with a thermometer with a protection tube in order to control the temperature of the reaction system. FIG.
It shows the outline of the above-mentioned cracking furnace, which is mainly composed of a radiating section 1 for heating and decomposing the raw material and a convection section 2 for collecting heat from the combustion gas. are doing. For example, the raw material 3 such as naphtha supplied to the cracking furnace is mixed with the diluted steam 4 in the convection section 2 and heated to about 600 ° C. by convective heat transfer with the combustion gas. Then, it is supplied to the reaction tube of the radiating section 1 and burned at about 800 ° C.
Heating to the above high temperature induces a thermal decomposition reaction to produce an olefin. On the other hand, the generated cracked gas is cooled by a cooler 6 installed at the outlet of the reaction tube in order to stop the reaction in order to prevent excessive cracking, and sent to a downstream separation column 7. In the reaction of the cracking furnace, factors affecting the yield of olefins and the like include pressure, temperature, and reaction time. In order to control the temperature, which is one of the factors, a thermometer 8 is provided at the exit coil of the reaction tube in the decomposition furnace via a protection tube.

By the way, the inside of the above-mentioned reaction tube means that a decomposition gas containing fine carbon particles having a flow velocity of about 150 to 200 m / sec flows, and the carbon adhering to the inside of the reaction tube is periodically removed. It is characterized by a remarkable loss of wear due to the decoking operation for removal. This phenomenon also acts on the thermometer protection tube 21 inserted in the reaction tube outlet coil as shown in FIG. 2, so that this protection tube also undergoes severe wear reduction. For that purpose, conventionally, the operation of the decomposition furnace was stopped and the thermometer protection tube 21 was replaced or
Alternatively, a device has been devised in which the side of the fluid that is not thinned and opposite to the flow of the fluid is reset to face the flow. This is because if the thinning of the thermometer protection tube 21 progresses and the thermometer protection tube 21 is damaged, the decomposition gas inside the reaction tube leaks, leading to an accident. In the drawing, 22 is a reaction tube, 23 is a thermometer mounting hardware, and 24 is a flow of a hydrocarbon decomposition gas.

Conventionally, the following method has been adopted as a method for solving such a problem. (1) A surface thermometer is welded to the reaction tube outlet coil surface to control the temperature. (2) The length of the protection tube inserted into the reaction tube outlet coil is shortened, and the portion to be reduced in thickness is reduced. (3) Strengthen the material of the protection tube. However, in the above method (1), there was a difference between the temperature measured at the reaction tube outlet coil surface and the temperature of the fluid in the tube, and it was difficult to control the temperature. In addition, there is a problem that the thermocouple is severely deteriorated, and it is difficult to replace the thermocouple because the thermometer is fixed by welding. In addition, the method (2) has a problem that accurate temperature cannot be measured because the protective tube is not inserted to the center of the axis of the reaction tube, and that temperature variation is large. On the other hand, in the above method (3), the temperature conditions are severe, so that merely changing the material of the protective tube was not sufficient in suppressing the wall thickness reduction.

[0005] Further, as a conventional technique other than the above (1) to (3), hard chromium plating, a thermal spray coating of a hard alloy or carbide cermet, TiN, CrN, TiCN by a PVD method or a CVD method are formed on the outer peripheral surface of the protective tube. There has been a method of applying a hard surface treatment film such as a film. However, the film formed by the application of these methods is easily destroyed at an early stage by erosion by carbon particles, and in fact, the expected results are not obtained.

[0006]

As described above,
Conventional thermometer protection tubes used in olefin production pyrolysis furnaces are exposed to high-temperature hydrocarbon cracking gas,
There has been a problem that erosion damage is liable to occur due to collision of hard carbon particles flying at a high speed, and the life is short. In particular, the thermometer protection tube not only protects the thermometer from mechanical external pressure but also plays a role in accurately and promptly transmitting the ambient temperature. Therefore, the protection tube is usually made of a metal member having good thermal conductivity. However, metal (alloy) members are softened in a high-temperature environment, and are easily damaged by erosion when they come into contact with carbon particles flying at high temperature and high speed. On the other hand, a method of improving the erosion resistance by treating the surface of the metal protective tube is conceivable. However, there are many cases where the thermal conductivity is impaired to deteriorate the measurement performance. The present invention seeks to overcome these problems.

Therefore, a main object of the present invention is to propose a surface treatment technique for manufacturing a thermometer protection tube which is excellent in heat conductivity and heat resistance and erosion resistance. Another object of the present invention is to establish a technology capable of accurately measuring a temperature and advantageously producing a metal protective tube having a long life, thereby improving the productivity of petrochemical raw materials such as olefins and maintaining the equipment. To reduce emissions.

[0008]

According to the present invention, the prior art is
To solve the above mentioned problems,
Heat and erosion resistance
Made thermometer protection tube that is excellent and has good thermal conductivity
Build.BookThe invention is resistantHot goldGenusProtection tubeOn the surface of the real
In an atmosphere that does not contain oxygen,Cr AlloyMetal bike
530 wt% includedRemainingRigas Cr_ThreeC_TwoCarbide
-Met powderDecompressionBy plasma spraying,
Part or all of metal Cr in metal binderTo Cr
₂₃ C ₆ , Cr ₇ C _Three Or Cr ₃ C _Two Such as hard reactive chrome charcoal
Change into a compound Cr ₃ C _Two Dispersed in the matrix
BecomeForming a hard chromium carbide cermet spray coating
A method for manufacturing a protective tube for a measuring instrument, characterized in that:

(2) In the present invention, prior to thermal spraying, it is preferable to preheat at least the surface of the metal member at a temperature of 500 to 900 ° C. in an atmosphere substantially free of oxygen, preferably in a reduced pressure atmosphere. . (3) In the present invention, after thermal spraying, in an atmosphere containing substantially no oxygen, preferably in a reduced pressure atmosphere 500 to 900
By performing post-heating at a temperature of
It is preferred to promote the conversion of the chromium to the reactive chromium carbide. ( 4 ) That is, according to the present invention, when plasma spraying Cr ₃ C ₂ cermet powder on an inert gas atmosphere containing substantially no oxygen on the surface of the metal member, the metal member is heated to 500 to 900 ° C.
Either pre-heating or post-heating after film formation /
Or by applying both heat treatments,
By forming a sprayed coating in which some or all of Cr is changed to chromium carbide to a thickness of 50 to 800 μm, and modifying the coating so that the micro Vickers hardness of the coating is 1000 Hv or more on average, This is a method in which the entire coating is modified so as to exhibit hardness, densification, erosion resistance, and good thermal conductivity.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a protective tube for a measuring instrument according to the present invention will be described below with reference to an example of manufacturing a protective tube for a thermometer. (1) Regarding the method of coating the surface of a metal protective tube with a thermal spray coating, the environment in which the protective tube according to the present invention is used is at a high temperature as described above and under conditions where hard carbon particles collide at a high flow rate. And therefore the surface of the protective tube (sprayed coating)
Must be chemically stable and have excellent blast erosion resistance. In order to meet the demand for surface coating treatment, that is, to form a thermal spray coating, the inventors studied oxide ceramics, carbide cermets, and hard metals (alloy steels) as materials to be sprayed. As the thermal spraying method, an experimental study was conducted on a method using an electric arc as a heat source, a method using plasma or the like as a heat source, and a method using combustion energy of hydrogen or hydrocarbon and oxygen as a heat source. In particular, the selection of the thermal spraying method is important because even if the same thermal spraying material is used, since the heat source temperature and the flow velocity greatly differ, a large difference occurs in the properties of the formed film.

In this regard, the inventors first aimed at developing a suitable thermal spraying method by the following experimental research.
With some success, the present inventors have arrived at the present invention. The results of the experimental research are described below.

In this experiment, first, in order to determine the suitability of the sprayed material, various hard sprayed materials were formed on a substrate made of SS400 steel using various spraying methods to an average thickness of 300 μm. The sprayed coating was sprayed with Al ₂ O ₃ particles using 5 kgf / cm ² of compressed air (spray distance 500 mm), and the erosion resistance of the sprayed coating was qualitatively examined. Table 1 summarizes the results of this experiment. As shown in Table 1, the oxide ceramic sprayed coatings such as Al ₂ O ₃ and TiO ₂ were hard but brittle, and easily caused local exfoliation. However, the WC, Cr ₃ C ₂ cermet sprayed coating showed relatively good erosion resistance and was found to be the most suitable material for the purpose of the present invention. The self-fluxing alloy films did not show any peeling phenomena due to wear alone. However, it was also found that these films were not suitable because they had a feature that their hardness was significantly reduced in a high temperature environment around 800 ° C.

[0013]

[Table 1]

Based on the above results, the inventors focused on carbide cermet material as a thermal spray material suitable for the present invention. In addition, the high-temperature stability of each of the above thermal spray materials was also examined. As a result, it was found that the WC cermet film was poor in heat resistance such as being oxidized and decomposed in an environment of 550 ° C. or higher. That is, as a material that is well suited to the method of the present invention, it is concluded that a powder material of Cr ₃ C ₂ cermet which is inferior in hardness and erosion resistance but excellent in heat resistance is preferable as compared with WC cermet. Reached.

(2) Regarding thermal spraying of Cr ₃ C ₂ cermet powder With the above progress, in the present invention, Cr ₃ C ₂ was used as a thermal spraying material for coating the protective tube surface. Therefore, in order to clarify the thermal spraying method for spraying this Cr ₃ C ₂ cermet powder to form a good coating, a thermal spray coating of about 150 μm thickness was formed, and the porosity, adhesion, The hardness was investigated.

Table 2 summarizes the test results. As can be seen from the results shown in Table 2, in the atmospheric plasma spraying method tested as a comparative example, with or without preheating,
Both adhesion and hardness were poor. On the other hand, the sprayed coating obtained by the high-speed flame spraying method has a small porosity even without preheating, and has a hardness of 750 to 850 Hv and an adhesion of 80.
Very high measured values of over MPa were obtained. However, the thermometer protection tube coated with the sprayed Cr ₃ C ₂ film formed by this method is connected to the olefin production equipment shown in FIG. 1 (gas temperature 650 to 800 ° C.).
When the test was conducted on an actual machine, most of the film had disappeared due to erosion by carbon particles in about 4 months of operation.

[0017]

[Table 2]

Therefore, the cause was investigated. As a result, the following was found. That is, although having a Cr ₃ C ₂ particles themselves are hard and erosion resistance, since the metal as a binder coexisting is softened in a high temperature environment, only the metal component is selectively subjected to erosion, resulting Cr ₃ It was found that the C ₂ particles lost their mutual binding force and were worn.

Next, the inventors have continued to study whether there is a method of hardening a metal component added as a binder in an environment in which a sprayed coating is formed. as a result,
Cr ₃ C using Cr or Cr alloy as binder metal
₂ Plasma-spray the cermet material in a substantially oxygen-free, non-oxidizing atmosphere, and
(0 ° C) for more than 10 minutes. Then, Cr ₃ C ₂
Free carbon contained in itself or in Cr ₃ C ₂ reacts with some or all of Cr added as a binder to form Cr ₂₃ C ₆ , Cr ₇ C ₃ or Cr ₃ C ₂ or the like. It has been found that the reaction chromium carbide changed to hard carbide results in a Cr ₃ C ₂ cermet spray coating having higher hardness. According to the researches of the inventors, such a result is impossible by a conventional general thermal spraying method, and is preferably performed under a non-oxidizing atmosphere containing substantially no oxygen, preferably under a reduced pressure plasma thermal spraying method. Is possible for the first time by the application of Cr ₃ C
₍₂₎ The hardness of the sprayed cermet coating was found to be as high as 1100-1250 Hv, almost comparable to WC cermet. (For example, test piece 2 in Table 2)

As described above, if oxygen is contained in the sprayed atmosphere during the spraying, Cr in the formed sprayed coating is
_{The surface of the 3} C ₂ particles and the binder metal component is oxidized, which hinders the carbonization reaction of Cr as the metal component, which is not preferable.

In the present invention, in order to further promote the carbonization reaction of Cr, the object to be sprayed (metal substrate) itself is heated (500 to 900 ° C.) prior to the thermal spraying.
By improving the adhesion of the thermal spray coating and reducing the residual stress of the thermal spray coating, a thick film can be formed. Also,
In order to further promote the carbonization reaction of Cr, it is preferable to post-heat to a high temperature of 500 to 900 ° C. even after thermal spray deposition. It was also found that such pre-treatment and post-treatment operations made the sprayed coating denser and significantly improved the thermal conductivity, and did not hinder the heat transfer to the thermometer.

In the present invention, as the metal component to be added to Cr ₃ C ₂ (or Cr ₂₃ C ₆ ), Cr or an alloy containing Cr (Cr-Ni, Cr-Co, Cr-Fe, etc.) is suitable. Single metals, such as Ni, Co, and Cu, which are difficult to generate carbides, are not suitable. The amount of the metal component added is 5 to 30
_{wt% (Cr 3 C 2 95~} 60 wt%), Cr contained in the metal component
The amount is suitably in the range of 5 to 100 wt%. If the metal component is less than 5 wt%, the adhesion of the sprayed coating and the bonding strength between particles are weak, and if it is more than 30 wt%,
Although the ductility of the film is improved, the hardness is lowered and the erosion resistance is poor, which is not preferable.

(3) Thermal Spraying Method Next, the thermal spraying environment according to the present invention may be any non-oxidizing atmosphere containing substantially no oxygen. In this sense, the reduced pressure plasma spraying method in which the air is prevented from being mixed by the inert gas, the preheating of the object to be processed, the post heat treatment,
Operations such as holding at a high temperature after thermal spraying are also easy and suitable. In addition, a desirable thermal spray coating can be formed if the condition of the thermal spray atmosphere is oxygen-free, for example, in the range of 50 to 1100 hPa of an inert gas (for example, He, Ar or the like).

The thickness of the Cr ₃ C ₂ cermet film formed under the above conditions is preferably in the range of 50 to 800 μm, particularly 200 to 800 μm.
500500 μm is preferred. If the thickness is less than 50 μm, the erosion resistance is poor, and if the thickness is more than 800 μm, no particular effect is observed.

The Cr obtained by applying such a method
₃ C ₂ cermet sprayed coating is a coating of hard and dense, in addition to excellent adhesion to the substrate, because it contains no pores or oxides impede heat conduction in said coating, extremely good Since it exhibits thermal conductivity, it was found to be extremely excellent as a surface coating technology for thermometer protection tubes.

The sprayed material used under the method of the present invention
The chromium carbide in the material has the chemical formula: Cr _ThreeC_TwoIs indicated by
A survey of commercially available carbide cermet materials showed that
Cr_{twenty three}C_Two, Cr₇C_ThreeEtc. are also contained, and these
Apply the present invention to those containing carbides
Is possible and strict Cr_ThreeC_TwoLimited to compounds only
Not.

The reason why the preheating temperature of the substrate and the temperature of the post heat treatment after the film formation were respectively 500 to 900 ° C.
If the temperature is 500 ° C or higher, there is an advantage that the substrate temperature does not decrease due to the effect of the plasma flame during thermal spraying, and the most effective temperature range for the carbonization reaction of metal Cr is 500 to 900 ° C. This is because the adhesion and hardness of the film are improved because of this. On the other hand, heating at 900 ° C. or more is difficult, and too high a temperature is not advisable because the decomposition of chromium carbide is promoted.

[0028]

EXAMPLE 1 In this example, in addition to the Cr ₃ C ₂ particles, Ni—Cu, Ni, Cr—N
A cermet material containing 25 wt% each of metal components such as i and Cr-Co was plasma sprayed to a thickness of 300 μm on an SUS410 substrate in an atmosphere of an Ar partial pressure of 100 hPa. Then, the Vickers hardness of the obtained thermal spray coating was measured. The thermal spraying was carried out for the presence or absence of preheating (550 ° C.) of the SUS410 substrate and for the presence or absence of heat treatment after film formation (holding at 700 ° C. for 15 minutes). Table 3 shows the results at this time. Thermal sprayed coatings with Ni-Cu and Ni added as metal components
The hardness of Nos. 1 to 8 was less than Vickers hardness of less than 1000 Hv even after preheating and post heat treatment. On the other hand, thermal spray coatings containing a metal binder containing Cr (Nos. 10 to 12,
14 to 16), the film hardness was 1000 or more after any of the preheating and post-heat treatment steps, indicating that the film was hardened. Even when the same thermal spraying material was sprayed, the thermal spray coating was not cured and the adhesive strength tended to be low unless the heat treatment was performed (No. 13).

[0029]

[Table 3]

Example 2 A cracking furnace for an ethylene production apparatus was operated with naphtha as a main raw material, a radiating section at 800 to 840 ° C., and a pressure of about 1 atm. Thermometer protection tube is made of stainless steel (Incoloy 8
00H), the following thermal spray coating was formed on its outer surface, and the surface was examined after being used for 6 consecutive months. 1. Test sprayed coating (1) Sprayed coating of the present invention Cr ₃ C ₂ -25 wt% Ni-Cr cermet is sprayed by reduced pressure plasma spraying and applied to a thickness of 350 to 400 μm, Cr ₃ C ₂ -30 wt% % Ni-Cr cermet is sprayed by a low pressure plasma spraying method to form a sprayed coating with a thickness of 350-400 µm, and then heat-treated at 700 ° C x 10h in vacuum. (2) Spraying of Comparative Example Coating JIS H8303 regulation SFNi ₄ Self-fluxing alloy is sprayed, and the film thickness is 1200 ~
After forming a thermal spray coating of 1500 μm, this thermal spray coating is subjected to fusing treatment in air, the above self-fluxing alloy thermal spray coating is subjected to fusing treatment in vacuum, 25 wt% Cr-70 wt% Fe-2 wt% B -3wt% Si alloy
Thermal spray coating, Cr ₃ C ₂ -25 wt% Ni-Cr cermet applied to a thickness of 800 μm by arc spraying, thermal spray coating applied to a thickness of 350 to 400 μm by high-speed flame spraying, Cr ₃ Thermal spray coating of C ₂ -30 wt% Ni-Cr cermet applied to a thickness of 350 to 400 μm by atmospheric plasma spraying,

2. Test Results The test results for this example are summarized in Table 4. As can be seen from these results, all of the thermal sprayed coatings of Comparative Examples (Nos. 3 to 7) disappeared due to erosion by carbon particles after 6 months of operation of the plant. 30 ~ 70μ for the base material coated with
m. On the other hand, the thermal spray coatings (Nos. 1 and 2) conforming to the present invention showed no change in appearance at all, and showed only a decrease of about 3 to 15 μm by micrometer measurement.

[0032]

[Table 4]

Example 3 In this example, the thermal conductivity of a thermal sprayed Cr ₃ C ₂ cermet coating conforming to the present invention was measured. The film for measurement is SS400
After forming a thermal sprayed coating having a thickness of 500 μm on the substrate, a disk-shaped sample having a diameter of 10 mm and a thickness of 1 mm was cut out together with the substrate and used for measurement. In addition, as a thermal spray coating for comparison, a Cr ₃ C ₂ cermet coating in the atmosphere and Ar gas without preheating the substrate,
A plasma sprayed coating of a 50 wt% Cr-50 wt% Ni alloy was used.

Table 5 shows the test results of this example. Even if a metal having excellent thermal conductivity was subjected to plasma spraying in air (Nos. 5, 6), the particles constituting the film were oxidized. The thermal conductivity was extremely low due to the formation of materials and the presence of pores. It was confirmed that this value hardly changed even at 500 ° C. In addition, these trends are observed for the plasma sprayed Cr ₃ C ₂ cermet film in the atmosphere, but the inert gas (Ar gas)
Regarding the film sprayed in the inside (No. 4), it is recognized that the thermal conductivity is slightly improved, probably because the formation of oxides is suppressed. On the other hand, the Cr ₃ C ₂ cermet coating (Nos. 1 to 3) of the present invention, which had been subjected to either preheating or post-heating in an inert gas, or both of them, had the best thermal conductivity even at room temperature. At 500 ° C, the tendency to further increase the thermal conductivity was clearly observed.The oxide film was not contained, and the film was densified by the sintering reaction due to preheating and post heat treatment. It can be seen that the improvement in the adhesiveness with metal and the carbide conversion reaction of metal Cr contribute to the improvement in the thermal conductivity.

[0035]

[Table 5]

[0036]

As described above, according to the production method of the present invention, a thermometer protection tube attached to an apparatus for producing olefins such as ethylene and propylene is provided with an average micro Vickers hardness of 1000 Hv or more. In addition to having high hardness, it is dense and excellent in erosion resistance, and it can be surface-treated so as to exhibit good thermal conductivity and conform to the present invention.

[Brief description of the drawings]

FIG. 1 shows a process line of a cracking furnace for an olefin production apparatus.

FIG. 2 shows a mounting state of a thermometer provided at an outlet of a decomposition furnace radiant tube.

[Explanation of symbols]

1 Radiation unit for raw material decomposition 2 Convection section for heat recovery 3 Raw naphtha line supplied to cracking furnace 4. Steam line supplied to the convection section 5 Burner for heating 6 Decomposed gas cooler 7 Decomposed gas component separator 8 Thermometer 21 Thermometer protection tube 22 Reaction tube 23 Thermometer mounting bracket 24 Flow direction of cracked gas

Continuation of the front page (56) References JP-A-54-65718 (JP, A) JP-A-56-62956 (JP, A) JP-A-5-295592 (JP, A) JP-A-1-1399749 (JP) JP-A-49-97733 (JP, A) JP-A-6-340958 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 4/00-4/18

Claims (3)

(57) [Claims] On the surface of the 1. A resistance Netsukin genus made protective tube, substantially in an atmosphere containing no oxygen, there is a metallic binder is a Cr alloy. 5 to 30 wt% unrealized residual Riga Cr ₃ C ₂ By subjecting the carbide cermet powder to low pressure plasma spraying, a part or all of the metal Cr in the metal binder is reduced to Cr ₂₃ C ₆ , Cr ₇ C
_To hard reactive chromium carbides such as ₃ or Cr ₃ C ₂
And forming a hard chromium carbide cermet sprayed coating formed by dispersing in a Cr ₃ C ₂ matrix . 2. Prior to plasma spraying, at least the surface of the metal member is placed in a substantially oxygen-free atmosphere at 500
The method according to claim 1, wherein the preheating is performed at a temperature of -900 ° C. 3. After plasma spraying, post-heating is performed at a temperature of 500 to 900 ° C. in a reduced pressure atmosphere substantially free of oxygen to promote the conversion of metal Cr in the sprayed coating to reactive chromium carbide. The method according to claim 1, wherein: